Soft-magnetic multilayer thin film for use in a thin-film magnetic head and a method of manufacturing the same

ABSTRACT

A soft-magnetic multilayer thin film produced by electroplating, wherein an anode-dissolution process is effected by intermittently applying a reverse d.c. bias current with respect to the plating-forward current. Involving the anode-dissolution process allows the formation of a re-dissolution effect layer differing in crystal structure from the plated film layer. A soft-magnetic multilayer thin film characterized by having a multilayer film structure which comprises a plated layer and a re-dissolution effect layer laminated to each other and which the plated layer is at least magnetically isolated. Further, a method of manufacturing a soft-magnetic multilayer thin film having a multilayer film structure magnetically isolated only through plating, which is offered by introducing the anode-dissolution process. In a thin-film magnetic head produced by using a soft-magnetic multilayer thin film, the soft-magnetic multilayer thin film serves as at least one of an upper magnetic core layer and a lower magnetic core layer.

This application is a continuation of now abandoned application, Ser. No. 08/144,436, filed Nov. 2, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a soft-magnetic multilayer thin film for use in a thin-film magnetic head for high-density magnetic recording, and also relates to a method of manufacturing the same.

2. Description of the Prior Art

As a soft-magnetic layer of a thin-film magnetic core to be used in a HDD (Hard Disk Drive)-oriented thin-film magnetic head for magnetically recording data with high density, a Permalloy magnetic thin film produced by an electroplating method has been most widely used, conventionally. The manufacturing method by electroplating has been hitherto utilized taking the advantage of its capability of enhancing accuracy of soft-magnetic thin-film magnetic core patterns. However, an electroplating method, as applied to thin-film magnetic head cores, has been limited to applications to a Permalloy (Ni-Fe alloy) magnetic thin film because of its difficulty in alloy plating. In this connection, it has been revealed that, with use of a large amount of electric current for alloy plating, it is possible to obtain multi-element soft-magnetic alloy thin films, composed of such as Co-Fe-Cr, Fe-Co-Ni-Cr alloy and the like through electroplating method, which the soft-magnetic alloy thin films are high enough in saturation magnetic flux density to be suitable for high-density recording magnetic heads.

A Permalloy magnetic thin film produced by the electroplating method or multi-element soft-magnetic alloy thin films with high saturation magnetic flux density obtainable by the electroplating method, in particular, plating with use of a large amount of electric current as above mentioned have been involved with problems as following. That is, there occur minute depressions or protruded abnormally grown spots on the thin film surface due to hydrogen foaming or the like, which may adversely affect the magnetic characteristics, for example by causing the coercive force of magnetic core thin-film layers to increase, or obstructing the movement of magnetic domain walls.

Meanwhile, it is known that a multilayer film structure at least magnetically isolated in the direction of film thickness of the thin film is effective to enhance the high-frequency characteristic and to prohibit the magnetic domain structure of a magnetic core from being subdivided within the thin-film plane, based on the magnetic domain evaluation of laminated-film cores composed of a soft-magnetic thin film such as of Permalloy and a thin non-magnetic layer obtained by deposition. However, any practical method has not been known yet by which the whole multilayer film can be prepared through electroplating.

SUMMARY OF THE INVENTION

Accordingly, an essential objective of the present invention is to provide a soft-magnetic multilayer thin film for use in a thin-film magnetic head, which can be obtained only through electroplating. Another objective of the present invention is to provide a manufacturing method for the same soft-magnetic multilayer thin film, capable of improving the magnetic characteristics and high-frequency characteristics and controlling or singularizing the magnetic domain structure of a magnetic core.

In order to achieve the aforementioned objective, the present invention provides a soft-magnetic multilayer thin film which comprises: one or more soft-magnetic plated thin film layers formed through plating; and one or more re-dissolution effect layers obtained through anode-dissolution each having its crystal structure different from that of the soft-magnetic plated film layer, the two types of film layers being alternately laminated each other, where the soft-magnetic plated film layers are magnetically isolated to each other by providing the redissolution effect layers alternately interlaminated therebetween. In the soft-magnetic multilayer film of the present invention, the re-dissolution effect layer resulting from anode-dissolution is amorphous.

The present invention also provides a method of manufacturing the same soft-magnetic multilayer thin film, which comprises: the step of intermittently effecting an anode-dissolution process in the course of forming the soft-magnetic plated film thereby to alternately form one or more re-dissolution effect layers between the soft-magnetic plated film layers through anode-dissolution; and the step of forming a soft-magnetic multilayer thin film in which the laminated soft-magnetic plated film layers are magnetically isolated to each other by the interlaminated re-dissolution effect layers.

In the method of the present invention, a target to be plated is positioned as a cathode in the electroplating method with a d.c. current forwarding the plating process (referred to as, "plate-forwarding current" hereinafter), while a d.c. bias current intermittently supplied in the reverse direction (referred to as, "reverse d.c. bias current" hereinafter) with respect to that of the plate-forwarding current is set in value to be smaller than the plate-forwarding current, where the target to be plated is subjected to electroplating process under the condition mentioned above.

This plating method makes it possible to obtain a soft-magnetic multilayer thin film having at least a magnetically isolated multilayer film structure which comprises one or more soft-magnetic plated film layers obtained by electroplating the target with the plate-forwarding current, and one or more re-dissolution effect layers each differing in crystal structure from the plated film layer, the re-dissolution effect layers being obtained with the reverse d.c. bias current under the condition that the d.c. bias current in the direction reverse to that of the plate-forwarding current is set to be smaller in value than the plate-forwarding current.

Therefore, according to the present invention, by intermittently effecting the anode-dissolution process in the course of electroplating film formation, one or more re-dissolution effect layers are alternately formed each having its crystal structure different from that of the soft-magnetic plated film layer, making it possible to form a soft-magnetic multilayer thin film having a multilayer film structure which the soft-magnetic plated layers are isolated at least magnetically to each other by providing the interposed re-dissolution effect layers. Further, it is possible to vary the thickness of each of the redissolution effect layer differing in crystal structure from the soft-magnetic plated film layer, depending on the time taken for supplying the reverse d.c. bias current for the anode-dissolution. Moreover, by introducing the anode-dissolution process a plurality of times in the whole process of forming the soft-magnetic plated film, it is made possible to form a soft-magnetic multilayer film which the number of the layers depends on the number of times of the introduction of the anode-dissolution process.

Furthermore, according to another feature of the present invention, the soft-magnetic multilayer film has at least a magnetically isolated multilayer film structure which comprises one or more soft-magnetic plated film layers and one or more re-dissolution effect film layers alternately laminated, each re-dissolution effect film layer having its crystal structure different from that of the plated film layer, and therefore the high-frequency characteristic and magnetic domain structure- within the thin film plane are largely affected. In more detail, generally in a single-layer thin film structure, since the state of the magnetic domain structure has a magnetic pole at an external position of the film and is unstable in energy, the magnetic domain structure of the film forms a magnetization loop within the film plane as shown in FIG. 6(a). In contrast, in a multilayer film structure having a plurality of magnetic thin layers and a plurality of nonmagnetic thin layers alternately laminated to each other, the magnetic domain structure thereof forms a magnetization loop in the film thickness direction of a pair of upper and lower layers as shown in FIG. 6(b), which the state of the magnetic domain structure is stable in energy. Thus, it has been accomplished to singularize the magnetic domain for the magnetic domain structure within the thin film plane and to improve the high-frequency characteristic by magnetostatically couplings among the multilayer laminated films in the direction of the film thickness.

Also, it is accomplished to improve the magnetic characteristic of the magnetic core in the case of applying the method of the present invention to the process of manufacturing thin-film magnetic head cores, while the output improvement especially on the high band region as well as improvement of noise reduction have been achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which:

FIG. 1 is a timing chart showing a way of applying a current in The electroplating process for manufacturing soft-magnetic multilayer films according to the present invention;

FIG. 2 is a schematic sectional view representing a soft-magnetic multilayer film structure obtained by the manufacturing method according to the present invention;

FIG. 3 is a schematic view representing a structure of a thin-film magnetic head provided with a soft-magnetic multilayer plated film of the present invention;

FIGS. 4(a) and 4(b) are schematic views showing an electroplating method of the present invention;

FIGS. 5(a), 5(b), 5(c) and 5(d) are views showing a process of manufacturing soft-magnetic multilayer films according to the present invention; and

FIGS. 6(a) and 6(b) are schematic views showing magnetization loops of a single-layer film structure and a multilayer film structure, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention is now described in more detail with reference to the drawings.

In a method of manufacturing a soft-magnetic multilayer thin film, anode-dissolution is intermittently effected in the course of forming the soft-magnetic plated film by electroplating to form a re-dissolution effect layer with a d.c. bias current intermittently supplied in the reverse direction with respect to that of a plate-forwarding current, where the reverse d.c. bias current is set in absolute value to be smaller than the plate-forwarding current. The re-dissolution effect layer has its crystal structure different from that of the soft-magnetic plated film layer. Then, alternately formed is a soft-magnetic multilayer thin film in which the laminated soft-magnetic plated film layers are magnetically isolated to each other by the interlaminated re-dissolution effect layers.

In more detail, as shown in FIG. 4(a), in the manufacturing method of the present embodiment, a target (i.e., substrate 3) to be plated is positioned as a cathode in the electroplating solution 9 while a Pt net 10 is positioned as an anode in the electroplating solution with supply of a d.c. current forwarding the plating process.

In the first step, as shown in FIG. 5(a), a plated film 1 is formed on the substrate 3 by electroplating with supply of a plate-forwarding current I₁ of a positive d.c. constant value as shown in FIG. 1, where the substrate 3 is positioned as the cathode and the Pt net is positioned as the anode of a d.c. current supply source 11.

Then, the positive terminal and negative terminal of the d.c. current supply source are reversed to each other as shown in FIG. 4(b), in other words, the substrate to be plated is positioned as the anode while the Pt net is positioned as the cathode. Under this condition, the plated film 1 just formed on the substrate 3 is partially dissolved in the plate solution with a reverse d.c. bias current I₂ of a negative constant value as shown in FIG. 1, which the process is referred to as, "anode-dissolution". In the anode-dissolution process, on the plated film 1, there is formed a re-dissolution effect layer 2 having its crystal structure different from that of the plated film layer 1 as shown in FIG. 5(b), where the absolute value of the reverse d.c. current I₂ is set smaller than that of the plate-forwarding current I₁.

Then, the positive and negative terminals of the d.c. current source 11 are reversed to each other to be back to the same state as the first state shown in FIG. 4(a), where a further plated film layer 1' is formed on the re-dissolution effect layer 2 as shown in FIG. 5(c).

Then, in the same manner, the positive and negative terminals are reversed to each other to further form a re-dissolution effect layer 2' on the plated film layer 1' as shown in FIG. 5(d).

These processes mentioned above are repeated thereby to alternately laminate the soft-magnetic plated layers 1 and the re-dissolution effect layers 2 to form a soft-magnetic multilayer thin film as shown in FIG. 2, where the soft-magnetic plated film layers 1 are magnetically isolated to each other by the interlaminated re-dissolution effect layers 2.

Table 1 lists the TEM analysis results and magnetic domain structures of Examples 1 through 16 of soft-magnetic plated films formed by an alloy plating process with Permalloy, Co--Fe--Cr ternary (three-element) alloy, Co--Fe binary (two-element) alloy, and Fe--Cr binary (two-element) alloy for the pattern of a top portion of a thin-film magnetic head-core, as various examples 1 through 16 where the reverse d.c. bias current I₂ is applied in the direction reverse to that of the plate-forwarding current I₁ of a constant value with which the plating is forwarded. The magnitude of current I (amplitude) satisfies the equation, I=I₁ +I₂, as shown in FIG. 1.

In table 1, "fcc" denotes a crystal-structure of a face centered cubic, "hcp" denotes of a hexagonal closed packed lattice, and "bcc" denotes of a body centered cubic.

From the results of Table 1, it was found that in either case of electroplating with Permalloy, Co--Fe--Cr ternary (three-element) alloy, Co--Fe binary (two-element) alloy, and Fe--Cr binary (two-element) alloy, when the redissolution process is introduced by intermittently applying the reverse d.c. bias current, rather than the case of electroplating only with applying the plate-forwarding current, one or more re-dissolution effect layers 2 formed by the re-dissolution of an anode material as shown in FIG. 2 are alternately interlaminated between the soft-magnetic plated layers 1 grown with the plate-forwarding current thereby to form a soft-magnetic multiple layer laminated film, thus providing at least magnetically isolated multilayer film structure in which the soft-magnetic plated layers are magnetically isolated to each other by the interposed re-dissolution effect layers. In this method, the re-dissolution effect layer resulting from anode-dissolution was amorphous, which fact has been found remarkable as compared with the normal plating with only supplying the plate-forwarding current I₁ under the condition of I₂ =0. Also, singularization of magnetic domains has been accomplished by selecting conditions in the method of the present embodiment.

In this embodiment, it is to be noted that the re-dissolution effect layer resulting from anode-dissolution is identical in alloy composition to the soft-magnetic plated layer, otherwise, that the re-dissolution effect layer resulting from anode-dissolution contains iron and at least one element of cobalt, chrome, and nickel in alloy composition.

Table 2 list the results of the improvements in the soft-magnetization and high-frequency characteristic in the case of plating with Permalloy, Co--Fe--Cr alloy, Co--Fe alloy, and Fe--Cr alloy, when re-dissolution is effected with a reverse d.c. bias current I₂ to form the redissolution effect layer 2.

From the results of Table 2, it was found that in either case of plating with Permalloy, Co--Fe--Cr alloy, Co--Fe alloy, and Fe--Cr alloy, when re-dissolution is effected with intermittent supply of a reverse d.c. bias current I₂, the re-dissolution effect layer 2 formed by the redissolution of an anode is combined with a grown plate-forwarding layer 1 formed with the plate-forwarding current thereby to form a multilayer film structure, the multilayer film layers being at least magnetically isolated, which allows the resulting plated multilayer film to be soft-magnetized with improvement of its high-frequency characteristic.

In addition, discussions and further study were also made upon materials of Fe--Co--Ni, Fe--Ni--Cr, and Co--Fe--Cr--Ni alloy films. As a result, in any case, when the redissolution process with a reverse d.c. bias current I₂ is introduced, a re-dissolution effect layer 2 formed through the re-dissolution of an anode is combined with a soft-magnetic plated layer 1 grown with the plate-forwarding current I₁ thereby to form a multilayer film structure, where the soft-magnetic plated thin film layers are at least magnetically isolated by the re-dissolution effect layer, which allows the resulting plated multilayer film to be improved in soft-magnetization with its high-frequency characteristic.

Further, with use of the films of Permalloy, Co--Fe alloy, Fe--Cr alloy, Co--Fe--Cr alloy, Co--Fe--Ni alloy, Fe--Ni--Cr alloy, Co--Fe--Cr--Ni alloy for the magnetic core, an example of a thin-film magnetic head as shown in FIG. 3 was prepared. In the thin-film magnetic head, at least a part of a magnetic path constituting a magnetic circuit is implemented by using The soft-magnetic multilayer thin film of the present embodiment.

As shown in FIG. 3, the magnetic circuit is comprised of an upper magnetic layer 4 and a lower magnetic layer 7 forming a magnetic loop shown by arrows in the figure. In FIG. 3, the thin film magnetic head comprises a coil conductive layer 5 and a coil insulating layer member 6 included between the upper and lower magnetic layers 4 and 7 both formed on a non-magnetic substrate 8. That is, in a thin-film magnetic head produced by using a soft-magnetic multilayer thin film magnetically isolated from each other, the soft-magnetic multilayer thin film serves as at least one of an upper magnetic core layer and a lower magnetic core layer.

Evaluation was made upon input/output and noise thereof by using the thin-film heads each having a total film thickness of 2 μm (i.e., each of the upper and lower magnetic layers 4 and 7 having a thickness of 2 μm), a number of turns of the coil of 15 turns×2 layers, a gap length of 0.5 μm, a track width of 10 μm, and an HDD with a medium of 1300 Oe. Consequently, the thin-film magnetic head using the multilayer film as shown in FIG. 2 showed improved output characteristics especially on the high band region better than those using the single-layer film for the core of the head, and moreover showed noise reduction to a degree of significant difference.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention as defined by the appended claims, they should be construed as included therein.

                                      TABLE 1                                      __________________________________________________________________________     Material of                                                                           Material       TEM analysis result                                      plated of effect                                                                             I.sub.1                                                                            I.sub.2                                                                            Plated                                                                               Effect                                             layer  layer  (mA)                                                                               (mA)                                                                               layer layer Magnetic domain structure                    __________________________________________________________________________     Permalloy                                                                             Ni--Fe 100 0   fcc         Multiple domain within thin-                                                   film plane                                   Permalloy                                                                             Ni--Fe 100 30  fcc   Amorphous                                                                            Single domain except                                                           peripheral regions                           Permalloy                                                                             Ni--Fe 100 50  fcc   Amorphous                                                                            Single domain within pattern                 Permalloy                                                                             Ni--Fe 100 70  fcc   Amorphous                                                                            Single domain within pattern                 Co--Fe--Cr    100 0   fcc + hcp   Multiple domain within thin-                                                   film plane                                   Co--Fe--Cr    200 0   fcc + hcp   Multiple domain within thin-                                                   film plane                                   Co--Fe--Cr                                                                            Co--Fe--Cr                                                                            200 50  fcc + hcp                                                                            Amorphous                                                                            Single domain within pattern                 Co--Fe--Cr                                                                            Co--Fe--Cr                                                                            200 100 fcc   Amorphous                                                                            Single domain within pattern                 Co--Fe        100 0   fcc + bcc   Multiple domain within thin-                                                   film plane                                   Co--Fe Co--Fe 100 30  fcc + bcc                                                                            Amorphous                                                                            Single domain except                                                           peripheral regions                           Co--Fe Co--Fe 100 50  fcc   Amorphous                                                                            Single domain within pattern                 Co--Fe Co--Fe 100 70  fcc   Amorphous                                                                            Single domain within pattern                 Fe--Cr Fe--Cr 100 0   bcc         Multiple domain within thin-                                                   film plane                                   Fe--Cr Fe--Cr 200 0   bcc         Multiple domain within thin-                                                   film plane                                   Fe--Cr Fe--Cr 200 50  bcc   Amorphous                                                                            Single domain within pattern                 Fe--Cr Fe--Cr 200 100 bcc   Amorphous                                                                            Single domain within pattern                 __________________________________________________________________________

                  TABLE 2                                                          ______________________________________                                         Material                 Coercive                                                                              Magnetic                                       of plated                                                                               I.sub.1 I.sub.2 force  permeability                                   layer    (mA)    (mA)    (Oe)   1 MHz 10 MHz                                   ______________________________________                                         Permalloy                                                                               100     0       0.5    1921  1156                                     Permalloy                                                                               100     30      0.3    2990  1539                                     Permalloy                                                                               100     50      0.3    3127  1743                                     Permalloy                                                                               100     70      0.15   3539  2156                                     Co--Fe--Cr                                                                              100     0       20     253   179                                      Co--Fe--Cr                                                                              200     0       11     435   273                                      Co--Fe--Cr                                                                              200     50      3      856   530                                      Co--Fe--Cr                                                                              200     100     1      1036  785                                      Co--Fe   100     0       1.35   1574  1187                                     Co--Fe   100     30      0.7    1532  1358                                     Co--Fe   100     50      0.4    1635  1479                                     Co--Fe   100     70      0.35   1775  1650                                     Fe--Cr   100     0       0.9    1668  1445                                     Fe--Cr   200     0       0.5    1756  1563                                     Fe--Cr   200     50      0.35   1797  1624                                     Fe--Cr   200     100     0.3    1853  1763                                     ______________________________________                                     

What is claimed is:
 1. A soft-magnetic multilayer thin film having a multilayer film structure which consists essentially of:a plurality of soft-magnetic plated film layers having a crystal structure and produced by electroplating a substrate to produce a soft-magnetic film thereon, and an amorphous re-dissolution effect layer produced by subjecting said soft-magnetic plated layer to anode redissolution by reversing the current in said electroplating being interposed between and laminated to each of said soft-magnetic plated film layers by said anode re-dissolution, each of said re-dissolution effect layers having a crystal structure different from that of said soft-magnetic plated film layer, and wherein said soft-magnetic plated film layers are magnetically isolated from each other by said re-dissolution effect layers.
 2. The soft-magnetic multilayer thin film as claimed in claim 1, wherein said soft-magnetic plated film layer is made of a multi-element alloy composed of iron and at least one element selected from the group consisting of cobalt, chromium, and nickel.
 3. The soft-magnetic multilayer thin film as claimed in claim 1, wherein said re-dissolution effect layer resulting from anode-dissolution is identical in alloy composition to said soft-magnetic plated layer.
 4. A thin-film magnetic head, wherein at least a part of a magnetic path constituting a magnetic circuit is implemented by using the soft-magnetic multilayer thin film as defined in claim
 1. 5. The soft-magnetic multilayer thin film as claimed in claim 2, wherein said re-dissolution effect layer resulting from anode-dissolution contains iron and at least one element selected from the group consisting of cobalt, chromium, and nickel in alloy composition. 